This invention relates generally to a serial printer of the type using a wire dot printing head and more particularly, to a serial printer which provides a precision construction which is readily assembled, disassembled and adjusted. In many constructions of serial printers of the prior art, the print head is fixed on a head carriage by means of screws. Using screws makes it difficult to mount the print head on the carriage and to remove it from the carriage. Also, in serial printers using wire dot print heads, the print heads must be replaced when wires have been worn away through printing. Conventional methods however have the disadvantage that mounting and removing of the print head are difficult. Additionally, careful measurement and adjustment of the distance between the print head and the platen are necessary in order to properly position the print head.
In U.S. Pat. No. 3,958,254, an electronic printer is disclosed wherein mounting and dismounting of the print head to and from the head carriage is facilitated. Though the mounting and removing of the print head according to this patent is easier than it is in constructions where the print head is fastened by screws, there are disadvantages in that many parts are necessary for fixing the print head and the shapes of the parts are intricate. When using a print head of the impact type, for example, a wire dot printer, this construction makes it difficult to keep the head fixed properly because of the impact of the printing process.
In printers, there is also a need for adjusting the gap between the print head and the platen. Such an adjustment is necessary to accommodate the use of different page thickness or a different number of copies, or the magnitude of the impact force during printing. In U.S. Pat. No. 4,189,244, an adjustment device for the platen gap is disclosed. However, in this construction, there is the disadvantage of high cost because the mechanism for rotating an offset shaft is complicated and requires many parts.
In the prior art, an endless belt having teeth is frequently used to drive a head carriage on which a printing head of a serial printer is mounted. However, with a timing belt there is difficulty in connecting the belt to the head carriage because it is endless. As a result of this endless construction, it is usually necessary that another component be used for setting the timing belt on the head carriage and this component is generally fixed by screws or the like. Otherwise, a timing belt which is cut, that is, which is not endless, is used in order to reduce the difficulty of connecting the timing belt to the head carriage. These approaches to the problem have disadvantages in that the structure connecting the timing belt to the head carriage is complicated and costly to produce. Moreover, assembly and disassembly of the structure are difficult.
Because printing is carried out by moving the print head laterally relative to the print medium, the print head is electrically connected by means of a flexible print cable. A wire dot print head and flexible print cable have been connected in such a way that a coil for driving wires is fixed on a rigid circuit board and the rigid circuit board is combined with the flexible print cable by using a connector, or the like. Therefore, this construction uses many components and many portions which must be connected. As a result, the reliability of the products completed using these components is low, and the cost is high to provide the parts and to assemble them in production. In U.S. Pat. No. 4,265,549, a flat flexible printed circuit cable for a print head is disclosed. In this patent, a thin flexible printed circuit cable encircles the solenoid assemblies and has embedded therein thin flexible wires each terminating at one end in a connection with a solenoid assembly. The opposite ends are connected to a connector plug mounted on the cable assembly and adapted to releasably receive a mating connector. But, in accordance with this construction, the form of the flat flexible printed circuit cable is very complicated so as to make it tiresome to construct, assemble and repair.
What is needed is a serial printer which provides for simple assembly and disassembly of the print head from the carriage, simple and positive positioning of the carriage to the driving belt, simple means for adjusting the gap between the head and the platen and a simplified electrical cable connecting the print head to the control system.